Our ability to visually identify small objects or to read while we walk, run, or ride depends critically on the vestibulo-ocular reflex (VOR) to minimize image motion across the retina. The basic organization of this reflex appears deceptively simple, a three neuron arc that processes sensory signals to produce eye movements (E + H = O). We now know, however, that the 3 neuron arc is but one of the many pathways used to produce the VOR, and that other, less direct, pathways process essential signals for the reflex. At least 4 nuclear groups, identified by their direct connections with vertical oculomotoneurons, are involved in the vertical VOR: the vestibular nuclei, the vestibular y-group, the INC, and the rMLF. We know the discharge patterns or signals carried by neurons in these nuclei, and we can make reasonable assumptions about what signal is conveyed to motoneurons by each of these premotor sources. Our long range goal is to analyze how the oculomotor system generates these signals, and how they are combined to produce normal vertical conjugate eye movements, but this proposal is aimed specifically at the contribution of the INC and the vestibular y-group. These nuclei carry signals closely related to slow phase eye velocity and to eye position during the vertical VOR, smooth pursuit, and fixations. The vertical VOR is an integrated response to afferent signals arising from the semicircular canals, the otolith organs, and the visual system. The secondary goal of this proposal is to learn how these afferent signals interact and are combined to produce the vertical VOR. These aims are specifically delineated as research needs and opportunities in conjugate eye movement control in the NIH publication, Vision Research: A National Plan 1983-1987.